Immersion freezing system



June 8, 1965 J. J. RENDOS 3,137,514

:MMERSION FREEZING SYSTEM Filed Nov. 29, "1963 V C P REG.

STEAM INTAKE COOLING I08 TOWER AIR INTAKE I28 INVENTOR. JOHN J. REA/DOS bmmwwwwt A 7' TORNEY United States Patent 3,187,514 IMMERSION FREEZING SYSTEM John J. Rendos, Millington, N.J., assignor to Air Reducfion Company, Incorporated, New York, N.Y., a corporation of New York Filed Nov. 29, 1963, Ser. No. 326,671 15 Claims. (Cl. 62-63) This invention relates to immersion freezing systems and more particularly to systems using a cryogenic liquid refrigerant, more especially nitrous oxide.

An object of the invention is to recycle and purify the vapor which evolves from the immersion bath due to the heat received by the refrigerant during the freezing process, thereby conserving the refrigerant and separating therefrom the air or other impurities introduced by the articles being frozen or otherwise mixed with the vapors above the bath.

A feature of the invention is a two-stage apparatus and method for recycling and purifying the refrigerant, wherein in the first stage a major portion of the vapor is condensed to liquid state and returned to the immersion bath. The residual vapors which retain the contaminating impurities are further cooled in the second stage to solidify substantially all the remaining refrigerant, thereby separating the refrigerant from contaminating vapors that are noncondensible at the freezing temperature of the refrigerant. Subsequently, the separated solidified refrigerant is warmed and returned to the immersion bath.

In its most preferred embodiment, the immersion freezing system according to the present invention includes nitrous oxide as the immersion refrigerant, them-anipulative steps and the nitrous oxide refrigerant cooperating to afford a unique and highly advantageous system. The condensation of a major portion of the vaporized refrigerant free of impurities in the first stage of the recycle effectively concentrates the impurities in the minor residual portion of the vaporized refrigerant and substantially reduces the energy requirement and complexity of ultimately separating the impurities. The nitrous oxide is characterized by its ability to solidify at reduced temperature in the presence of the remaining gaseous impurities which include predominantly atmospheric constituents of the vapor and substantially reduces the energy requirement and complexity of ultimately separating the impurities. The nitrous oxide is characterized by its ability to solidify at reduced temperature in the presence of the remaining gaseous impurities which include predominantly atmospheric constituents and hydrocarbons and is thus readily recovered free of the contaminating constituents by condensation in the second state of the recycle.

A further feature is the use of the cold noncondensible vapors to cool and condense vapors of the refrigerant in a vapor space over the immersion bath and in the vapor space in a storage container over a reservoir of the refrigerant, thereby reducing vapor pressure in. these vapor spaces and reducing evaporation.

Another feature is the use of the cold noncondensible vapors in direct heat exchange with articles about to be immersed, thereby precooling the articles and conserving refrigeration.

Other features, objectsand advantages will appear from the following more detailed description of an illustrative embodiment of the invention, which will now be given in conjunction with the accompanying drawing, the single figure of which is a flow sheet of the illustrative embodiment.

In the drawing, an enclosed insulated tank is shown partly filled with liquefied gas, preferably nitrous oxide. A conveyor belt 12 is provided for conveying articles to be frozen into the tank, immersing the articles in the cold liquid for a predetermined period of time, and removing 3,187,514 Patented June 8, 1965 ice the frozen articles from the tank. The belt 12 may be supported in any suitable manner, such as on rollers 14, and propelled by known means, not shown. The body or bath of cold liquid is shown at 16. The duration of immersion may be regulated in any suitable manner as by controlling the travel rate of the belt.

The bath is preferably maintained at a pressure slightly greater than atmospheric to prevent air infiltration. Articles or packages to be frozen are shown diagrammatically at 18. Objects may be moved into and out of the tank through suitable vapor locks, e.g., through vestibules with double doors, to reduce loss of refrigerant vapor during entrance'and exit.

In order further to conserve the refrigerant, the vapors formed due to the cooling and freezing of the articles are drawn off into a novel combination of external equipment designed to separate'the refrigerant vapor from air or other contaminants, and to condense and recover the refrigerant for re-use.

For this purpose, a vapor compressor 20 has its input side connected through a conduit 22 with the vapor space 17 above the bath 16. The vapor compressor 20 is controlled by a pressure switch 24 which turns on the compressor when the vapor pressure above the bath exceeds the desired predetermined pressure and turns the compressor oif whenever the vapor pressure falls to the predetermined'v-alue. This is a precaution to prevent the compressor from creating a vacuum in the tank 10 if for any reason the freezing process stops, for any period of time, long or short.

The output of the vapor compressor 20 is delivered to a main condenser 26 by way of a conduit 28. For the condenser 26, a shell and tube type of heat exchanger is appropriate, with the conduit 28 opening into the tube header at the top. The shell of the condenser 26 is cooled by fluid circulating in the shell, as from a refrigerator 30, having a coolant delivering conduit 32 opening into the lower part of the shell and a return conduit 34 for coolant emerging from the upper part of the shell. The compressed coolant from the refrigerator 30 is cooled as by means of a cooling tower 36 connected with the refrigerator by a warm conduit 38 and a cold conduit 40.

The vapors from the conduit 28 are partially condensed in the condenser 26, the condensate being substantially pure liquid nitrous oxide in the case of a nitrous oxide freezer. The condensate is fed back into the tank 10 by gravity through a trapped and valved conduit 42, opening at the bottom of the condenser 26. The uncondensed vapors are forced from the bottom of the condenser 26 through aconduit 44 to a two-way valve 46 and thence to one or the other of a pair of scavenging heat exchangers 48 and 50. In the figure, the conduit 44 is shown connected through the valve 46 and a valved conduit 52 to the exchanger 48. Alternatively, a connection may be made by a valved conduit 53 to the exchanger 50. The

. scavenging exchangers 48 and 50 are used one at a time alternately for freezing out the remaining refrigerant fed in through the conduit 44. The exchanger not performing the freezing function at a given time is used for thawing out the frozen refrigerant. These exchangers may be of the shell and tube type. The vapors to be condensed and frozen may be passed through the tubes. The shell portion may be alternately cooled and heated by any suitable means. For these purposes, there is shown in the figure a refrigerator 54 for supplying coolant to either shell by way of a delivery conduit 56 and a return conduit 58. By means of a pair of two-way valves 60 and 62, the coolant may be switched from one exchanger to the other. The refrigerator 54 is connected to the cooling tower 36 by a warm conduit 64 and a cold conduit 66. For the thawing operation, a separate heating coil 63 is provided I in the shell portion of the exchanger 48 and a similar coil 70 in the exchanger t By means of a two-way valve 72 V and a valved conduit 74 a source of heated air may be connected at appropriate times tothe heating coil 68. Another valved conduit 76 is shown similarly connecting the heated air source to the heating coil '71) under the control of the valve 72. Any suitable heating source may be used. For example, as shown in the figure, atmos pheric air is indirectly heated by steam in a heat exchanger '78. The air isdrawn into a blower 89 through an air intake 82 and passed through a conduit 84 into the cold end of the exchanger 78. The heated air from the exchanger 78 is fed through a conduit 86 to the valve 72 for switching into one or the other of the heating coils 68 and 70. Steam is passed through a separate passage in the exchanger 78, countercurrently to the air, from a steam intake 88, and exhausted to atmosphere through a regulator valve 90, regulated by back pressure at the inlet side of the valve. Exhaust air from the heating coils 68 and 70 is vented to the atmosphere by vent conduits 92 and 94, respectively.

Solidified refrigerant in the form of ice or snow in the bottom of exchanger 48 or 56, when melted, is' fed by gravity through the trapped and valved conduits 96 and 98, respectively, to the tank 10. Uncondensed vapors from the exchangers 48 and 51B are vented through conduits 100 and 102, respectively, either of which conduits may be switched by means of a two-way valve 104, through a pressure-regulated valve 106 to a conduit 1%.

The valve 106 is regulated by back pressure at its inlet side.

A reservoir of liquefied gaseous refrigerant may be maintained in a suitable container 110, wherein the body of liquid is shown at 112 with a vapor space 111 above.

The conduit 108 is connected to a condensing coil 114 V in the vapor space 111 of the container 111) and thence through another condensing coil 116 in the vapor space 17 of the tank 10, to a nozzle 118 positioned to play a stream of cold vapor upon articles 18 previous to the entry of each article into the tank 10.

Circulation of the liquid refrigerant about the articles to be frozen is provided by means of a pump 120 the input side of which is connected to the bottom of the tank 10 through a conduit 122, and the output side of which is connected through a filter 124 and valved conduits 126 and 12$ to the liquid body 16. A third conduit 1130 leads from the output side of the pump 120 to the bottom portion of the container 110. A valved conduit 132, which also includes a level control valve 134, connects the lowerportion of container 110 to the lower portion of the tank 10. The conduit 132 is useful for supplying make-up refrigerant from the container to the tank 10 as needed under the control of level control means136. When the valved conduits 126, 128 and 132 are closed off, the pump 120 maybe used to pump the body of refrigerant 16 into the container 110, e.g., when it is desired to drain the bath 16 for purposes of cleaning the tank 10, or for any shutdown periods. The filter 124 serves to remove solid contaminants such as may enter the tank along with or become detached from the articles 18 being frozen.

In the case. of foodstuffs, e.g., bakery goods, the filter 124 may serve particularly to remove crumbs and broken fragments. p

In an illustrative embodiment of the above-described system, bakery products used as an example, but not limiting the apparatus to such use are placed upon the conveyor belt at a temperature of about 80 F., immersed in liquid nitrous oxide for a period of about 20 minutes,

whereupon the products come out frozen at an internal, temperature of about 0 F. The bakery products are passed through the immersion bath at a rate of about 5000 poundsper hour. Vapor in the space above the immersion bath is drawn into the vapor compressor at a tempera-' ture of about l28 F. and delivered to the main condenser at about 90 F. The vapor compressor has a capacity of about 520 standard cubic feet per minute and requires about 10 brake horsepower to, operate;

The higher temperature refrigerator is a 48-ton Freon unit requiring about 460 brake horsepower to operate and maintain a temperature of about -132 F. in the expanded coolant. This refrigerator cools the vapor in the main condenser to about same temperature, 128 F., as that of the vapor space 17 in the'freezer, condensing to liquid the major part of the nitrous oxide in the vapor and returning the liquefied nitrous oxide directly to the immersion bath.

The uncondensed vapors leaving the main condenser at about -l28 F. are cooled in the scavenging exchanger to about 180 F. by means of the low temperature refrigerator'which isa much smaller, 2.1 ton Freon unit, requiring 26 brake horsepower to operate, and maintaining its expanded coolant at about l F. The uncondensed vapors leaving the scavenging exchanger comprise about 5.2 standard cubic feet per minute of air and only about 0.29 standard cubic feet per minute of entrained nitrous oxide.

For the scavenging stream in the exchanger, air is supplied from the atmosphere by a blower which requires about 12 brake horsepower to operate. The air stream is heated by steam supplied to the deriming heater (exchanger 78) at a rate of about 1.03 pounds per minute at a pressure of about 10 p.s.i.g.

The reservoir of liquid nitrous oxide is kept in a standard storage tank holding about 2860 gallons. The pump for circulating and transferring the liquid nitrous oxide has a capacity of about 30 gallons per minute and requires about 1.5 brake horsepower to operate. While an illustrative form of apparatus and a method in accordance with the invention have been described and shown herein, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention. For example, while the invention has been described in connection with the provision of an immersion bath in which the articles to be frozen are immersed for contact with the liquefied refrigerant, it will be understood that such contact might be accomplished and air effective immersion produced by relying primarily upon a spraying of the liquid refrigerant on the articles.

I claim: 1. In an immersion freezing system, in combination, means forming an immersion chamber containing an immersion bath of liquefied gas refrigerant and means for presenting articles in said chamber for immersion in said bath, means for condensing a major portion of vaporized refrigerant arising from the immersion bath, means for returning said condensed vapor to the bath, means for further cooling and solidifying substantially all of the residual vaporized refrigerant, thereby separating said refrigerant from uncondensed impurities, means for subsequently separately warming said solidified refrigerant, and'means for returning said warmed refrigerant to the bath. 2 2. Apparatus in accordance with claim 1, together with a storage container for liquid refrigerant, means to supply liquid from said container to the immersion bath as needed, and means in the vapor space of said storage container and cooled by said cold uncondensed impurities for partially condensingvapor in said storage container, thereby reducing vapor pressure thereinr 3. Apparatus in accordance with claim 1, together with a pressurized container for the immersion bath, and means in the vapor space of said container and cooled by said cold uncondensed impurities for partiallycondensing va- 23 articles about to be immersed, thereby precooling said articles and conserving refrigeration.

5. Apparatus in accordance with claim 1, including means for circulating liquid refrigerant from and to said immersion bath and removing solid foreign particles from said refrigerant.

6. Apparatus in accordance with claim 5 wherein said means for circulating liquid includes pumping means, a filter, means for delivering the filtered liquid to a storage vessel containing a supply of said liquid refrigerant and means responsive to the level of the immersion bath in said immersion chamber for delivering liquid refrigerant from said storage vessel to said immersion chamber.

7. In a freezing system employing liquid nitrous oxide as refrigerant, including a freezing chamber means for contacting said liquid nitrous oxide with articles to be frozen thereby, and means for recycling and purifying the vaporized refrigerant,

comprising,

in combination,

means for condensing a major portion of the nitrous oxide in the vapor evolving from the freezing process,

means for returning said condensed vapor to said freezing chamber,

means for further cooling the remaining vapor, thereby to solidify residual nitrous oxide and to separate the solidified nitrous oxide from uncondensed impurities,

means for subsequently warming said separated solidified fraction,

and means for returning said warmed solidified fraction to said freezing chamber.

8. The method of recycling and recovering a cryogenic liquid refrigerant, which method comprises the steps of condensing a major portion of vaporized refrigerant arising from the body of liquid, returning condensed liquid refrigerant to the said body of liquid, further cooling and solidifying substantially all of the residual vaporized refrigerant, thereby separating said refrigerant from uncondensed impurities, and separately warming said solidified refrigerant to recover a further portion of the refrigerant.

9. The method of recycling and recovering a cryogenic liquid refrigerant, which method comprises the steps of compressing vaporized refrigerant arising from the body of liquid, cooling and condensing said compressed vapors at a temperature intermediate between the condensing temperature and the freezing temperature of the refrigerant, returning condensed liquid refrigerant to the said body of liquid, further cooling the residual uncondensed vapors to a temperature below the freezing point of the refrigerant, thereby solidifying substantially all of the refrigerant previously uncondensed and separating the refrigerant from uncondensed impurities, subsequently Warming said separated solidified refrigerant, and returning said warmed refrigerant to said body of liquid.

10. In a process of freezing articles by immersion in a cryogenic liquid bath, the steps of compressing vapors arising from the bath, condensing said compressed vapors, returning refrigerant so condensed to the bath, further cooling and solidifying residual uncondensed vapors, thereby separating refrigerant from uncondensed impurities, subsequently Warming said solidified refrigerant and returning the same to the immersion bath, passing the cold uncondensed vapors in indirect heat exchange with vapors above a body of said liquid refrigerant to at least partially condense said last-mentioned vapors, and therefter blowing said cold noncondensible vapors over articles about to be immersed in said bath to precool said articles.

11. In an immersion freezing system, in combination, means forming an immersion chamber containing an immersion bath of a liquefied gas refrigerant, means for presenting articles in said chamber for immersion in said bath, means for separating vaporized refrigerant arising from the immersion bath from impurities therein, means for returning the purified refrigerant to the bath, a storage container for liquid refrigerant, means to supply liquid from said container to the immersion bath as needed, and means in the vapor space of said storage container and cooled by said impurities for partially condensing vapor in said storage container, thereby reducing vapor pressure therein.

12. Apparatus in accordance with claim 11, together with means to spray said articles about to be immersed with said impurities, thereby precooling said articles and conserving refrigeration.

13. In an immersion freezing system, in combination means forming an immersion chamber containing an immersion bath of a liquefied gas refrigerant, means for presenting articles in said chamber for immersion in said bath, means for separating vaporized refrigerant arising from the immersion bath from impurities therein, means for returning the purified refrigerant to the bath, and means for spraying said impurities upon said articles to be immersed, thereby precooling said articles and conserving refrigeration.

14. In a process of freezing articles by immersion in a cryogenic liquid bath, the steps of compressing refrigerant arising from the immersion bath in vapor form, separating impurities from the refrigerant, returning the impurity-free refrigerant to the bath, and passing the impurities remaining in heat exchange with vapors above said liquid bath to at least partially condense said lastmentioned vapors.

15. The process as set forth in claim 14, including the step of thereafter blowing the impurities over articles about to be immersed in said bath to precool said articles.

References Cited by the Examiner UNITED STATES PATENTS EDWARD J. MICHAEL, Primary Examiner. 

10. IN A PROCESS OF FREEZING ARTICLES BY IMMERSION IN A CRYOGENIC LIQUID BATH, THE STEPS OF COMPRESSING VAPORS ARISING FROM THE BATH, CONDENSING SAID COMPRESSED VAPORS, RETURNING REFRIGERANT SO CONDENSED TO THE BATH, FURTHER COLLING AND SOLIDIFYING RESIDUAL UNCONDENSED VAPORS, THEREBY SEPARATING REFRIGERANT FROM UNCONDENSED IMPURITIES, SUBSEQUENTLY WARMING SAID SOLIDIFIED REFRIGERANT AND RETURNING THE SAME TO THE IMMERSION BATH, PASSING THE COLD UNCONDENSED VAPORS IN INDIRECT HEAT EXCHANGE WITH VAPORS ABOVE A BODY OF SAID LIQUID REFRIGERANT TO AT LEAST PARTIALLY CONDENSE SAID LAST-MENTIONED VAPORS, AND THEREAFTER BLOW- 